1. Field of the Invention
The present invention relates to the correction of spinal columns, and in particular the present invention relates to a surgically implantable device for maintaining vertebral bodies of the spinal column in a desired relationship during healing of a portion of the spinal column.
2. Description of the Prior Art
Surgery is required to correct deformation or degeneration or damage to a human spinal column, and in certain procedures at least one of the intervertebral discs is removed from a damaged portion of the spinal column. Bone graft is prepared, which may include the patient's bone or bone from another source. The bone graft is placed in the position from which the damaged disc has been removed. At this point it is necessary to fix the relation of the vertebral bodies on each side of the bone graft to maintain the vertebral bodies in a desired relationship and to prevent load from being transmitted through the bone graft while it is fusing.
It is desired that there be axial adjustment of the implant plates to account for differences between various vertebrae and the positioning of the screws or studs which are threaded into the vertebrae. It is important that these plates be accurately located and maintained in fixed position with respect to the studs.
It is also desirable that the implant plates on each side of the spinal column be cross braced with relatively rigid curved cross braces to maintain the lateral alignment of the vertebrae during the fusion process.
A further desirable attribute of a vertebral implant is that there be an adjustment for angular misalignment of the studs and the implant plates at the time the studs are threaded into the vertebrae. This allows for a correction in the amount of stress that is on the implant after it is tightened together. If an implant is highly stressed when it is placed into position, it is not an uncommon occurance that a stud will break at the stress point. This of course is undesirable in the healing process and requires a second operation to replace the broken screw.
Accordingly, it is a principal object of the present invention to provide a vertebra structural implant for connecting two or more vertebral bodies in axial and lateral directions whereby healing of a bone graft between the vertebral bodies is enhanced.
It is a further object of the present invention to provide a vertebral structural implant in which there is a lateral cross brace between the longitudinally positioned implant plates placed along the vertebrae being fixed together.
Still another object is to provide means for compensating for angular misalignment between the stud and the implant plate to reduce stress on the stud when it is firmly fastened to the implant plate.
Still another object is to provide a vertebra structural implant which has axial adjustment between an implant plate and studs fixed to adjacent vertebrae between which a bone graft has been placed with means for locking the parts together in close axial alignment along with means for compensating for angular misalignment between the studs and the implant plate to reduce stress on the studs.
These and other objects and advantages will become apparent hereinafter.